This invention relates to the art of forging in general and, in particular, to an improved method of forging with the use of closed dies. The closed-die forging method according to the invention has particular utility in forming blanks of generally disc-like or annular shape into spur gears, internal gears, etc., among other objects.
In closed-die forging, long used in industry for mass production, a metal blank is formed by compressive force into a desired shape in a closed cavity defined by a set of dies or by a mating punch and die. Such closed-die forging presents a problem, particularly in cases where the die cavity is entirely closed, as in the fabrication of gear wheels. The problem arises from the fact that the metal becomes progressively harder to flow toward the end of the forging, demanding the exertion of a correspondingly greater force Thus a tremendous forging force has heretofore been required to cause the material to finally fill up the internal space of the dies. The final forging force has been so great as to deform or, in some cases, even rupture the dies and so has seriously hampered the manufacture of gear wheels and comparable articles with precision by the closed-die forging method.